Hydraulic hammers sometimes comprise several valves that are necessary, for example, in order to control a back and forth movement of the impact piston, to adapt the operating ratio and the output of the impact mechanism to certain operating states or to protect the impact mechanism from overload. For certain applications, for example, both a manual stroke switch-over (long stroke or short stroke) and a manual switch-over of the no-load stroke safety mechanism are required (normal mode or no-load stroke safety mechanism) that can be achieved as a result of two separately arranged and switchable valves.
According to the prior art designs are known, for example, where the functions stroke switch-over and no-load stroke safety are set up either via two separate valves or via one single valve.
In the case of a design with two valves, along with the long stroke line a separate short stroke line leads to the one valve and a separate no-load stroke line leads to the other valve that open at different positions (axially spaced apart) on the cylinder working surface. As a result, in the return stroke, the piston path between the theoretical impact position and the position at which the impact stroke is introduced, and the piston path in the impact stroke direction, between the theoretical impact position and the position at which the impact mechanism is shut off, are able to be chosen in a relatively free manner. A disadvantage is the large amount of installation space necessary for the two valves, the many lines leading to the valves and the high amount of expenditure on production connected thereto, which results in large outer dimensions, the impact mechanism being heavy in weight and high production costs.
As a result of the separate lines and the separate valves, the following switching combinations are possible:                Normal (long)—stroke normal mode        Normal (long)—stroke no-load stroke safety mechanism activated (shut off)        Short stroke—no-load stroke safety mechanism deactivated (normal mode)        Short stroke—no-load stroke safety mechanism activated (shut off)        
In the case of designs with one valve that controls both functions (stroke switch-over and no-load stroke safety mechanism), two control functions (short stroke and no-load stroke safety mechanism) are realized by the common use of one single line that, depending on the switching position of the valve, acts either as a no-load stroke line (shut off line) or a short stroke line. A disadvantage, however, is that the stroke length in the short stroke and the piston path between the theoretical impact position and the position at which the execution of a return stroke and further operating cycles is stopped (shut off) are dependent on one another and are not able to be freely chosen, which can have a disadvantageous effect on the function, the output and the installation space of the impact mechanism.
The following combinations are possible according to the known prior art when using one valve and one common line:                Normal (long) stroke—no-load stroke safety mechanism activated (shut off)        Normal (long) stroke—no-load stroke safety mechanism deactivated (normal mode)        Short stroke—no-load stroke safety mechanism deactivated (normal mode).        
In addition, hydraulic impact mechanisms sometimes comprise even more valves, for example, a pilot valve for actuating the control slide, a pressure relief valve or flow regulating valve in order to adjust or limit the output or the operating pressure of the impact mechanism. Said valves as well as the above-described stroke switch-over valves and no-load stroke safety valves have been installed up to now separately from one another in the impact mechanism components.